Gundogan has featured heavily this season, starting 20 Premier League matches out of 37 in a squad packed with midfield options.
However, he is known to be at a stage in his career where he expects to be in the starting XI every week and those assurances cannot be forthcoming at City.
While his club insist any talks would happen in the summer, it is understood that it has been communicated to the player that an extension to his existing deal is unlikely. And, given Gundogan's service, he has been given the opportunity to explore options elsewhere with 12 months remaining on his deal.
The Germany international, who cost £21m in 2016, was on Monday morning spotted in the private jet terminal at Manchester Airport.
Spanish giants Real Madrid preciously attempted to sign the 31-year-old when he was with Borussia Dortmund but the purpose of his trip was unclear, with City's players having been given two days off ahead of what is expected to be a title decider against Aston Villa on Sunday.
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